Anti-GBM nephritis, the prototypic autoimmune nephritis for which the kidney target antigen is well characterized, is a key system for discovery involving human kidney disease pathogenesis. Nephritogenic epitopes reside on alpha3 (IV) NC1 collagen within the glomerular basement membrane. Compelling recent discoveries indicate the existence of a crossreactive and previously unsuspected additional self-antigen involved in disease pathogenesis, as well as immunological links between diverse anti-collagen diseases. These findings indicate remarkable complexity in autoimmune disease regulation, the elucidation of which will provide new insights into disease onset, suppression, and arrest. The goals of this proposal are to identify this second antigen and the molecular basis of novel receptor-ligand interactions, and to explore their engagement in human autoimmunity and disease pathogenesis in vivo. This effort relies on cutting edge but validated technologies and cross-disciplinary collaborations. Specific Aim 1 will use state-of-the- art and complementary proteomics approaches to identify the unknown second antigen that engages and regulates pathogenic reactivity to alpha3(IV)NC1 collagen. Specific Aim 2 will use innovative computational prediction modeling to determine receptor-ligand structure, both to further inform Aim 1 and to provide new insight into potential environmental disease precipitants and overlapping autoimmune regulatory circuits. Specific Aim 3 will develop a humanized model to examine autoimmune responses in vivo in the context of a human immune system, using the NOD-scid-gamma strain for enhanced engraftment of hematopoietic cells. The model will also generate unique human immune reagents and tools, with the ultimate goal of providing a platform for preclinical testing to validate research findings and to test immune modulating interventions in vivo. PUBLIC HEALTH RELEVANCE: Autoimmunity affects an estimated 7% of the U.S. population and worldwide underlies most immune nephritis, a leading cause of chronic kidney disease affecting native and transplanted organs. This proposal examines new paradigms that emerged from the study of anti-GBM nephritis, the prototypic autoimmune nephritis for which the human kidney target antigen, alpha3(IV)NC1 collagen, is well characterized. Anti- GBM nephritis thus is a key system for discovery involving human kidney disease pathogenesis and immune regulatory networks. Moreover, anti-GBM autoimmunity contributes to disease in ANCA vasculitis, can be induced by immune modulating mAb therapies, and shares genetic and immunological links with anti-collagen II autoimmunity and rheumatoid arthritis. Thus the proposed studies, designed to find the root cause of these diseases, are anticipated to have broad clinical relevance. Novel insights and new tools can be applied to a large patient population to advance new diagnostic and therapeutic approaches!